The Duke of Cambridge has pulled out of attending the British Military Tournament so he can spend time with the Duchess as she recuperates after receiving treatment in hospital for a severe form of morning sickness.

On Saturday night William commented to guests at a charity function about the extent of his pregnant wife's illness.

Attending the Winter Whites Gala in aid of homeless charity Centrepoint, he wryly observed that its name should be changed to reflect the fact she had been suffering night and day.

The royal couple had both originally been due to attend Sunday evening's event, billed as "the largest display of military theatre in the world", but all of Kate's forthcoming public engagements were cancelled after she spent three nights at the King Edward VII's Hospital suffering from hyperemesis gravidarum earlier this week.

A St James's Palace spokesman said: "The Duke of Cambridge will no longer attend the British Military Tournament at Earls Court this evening, but will spend Sunday privately with the Duchess instead. It is well known that hyperemesis gravidarum often recurs and, until further notice, to allow the Duchess a degree of privacy during her pregnancy, we do not intend to offer regular condition checks or advise of routine developments associated with it."

Former Centrepoint chairman Michael O'Higgins said on Saturday night that William had joked that the name of Kate's illness should be changed.

Mr O'Higgins said: "He said they shouldn't call it morning sickness as it's a day and all night sickness."

The Duke, who is a patron of the charity, did not make any reference to the apparent suicide of nurse Jacintha Saldanha, 46, who fell for a hoax call by two Australian radio presenters.

As he chatted to guests at London's Royal Albert Hall for his first public engagement since it was announced he is to become a father, the Duke was offered many congratulations on the happy news.

The British Military Tournament raises funds to support a number of military charities including the Royal Navy & Royal Marines Charity, ABF The Soldiers' Charity and the Royal Air Force Benevolent Fund.